Collection of readback signal modulation data

A data storage system comprising:

• a read channel comprising:
• a normal operation mode in which the read channel is configured to decode a readback signal to obtain data bits;
• a test mode in which the read channel is configured to extract gain control loop data from the readback signal at a different sample rate than any gain control loop data extracted during the normal operation mode;
• and
• circuitry configured to disable an output of the data bits from a detector of the read channel during the test mode when the readback signal is being obtained from reading user data.

A method comprising:

• extracting at least one of gain control loop data or timing control loop data from a readback signal obtained from reading user data stored on a data storage medium instead of obtaining data bits from the readback signal, wherein:
• the data storage medium is a part of a data storage system having a read channel that operates in either a test mode or a normal operation mode, and the extracting at least one of gain control loop data or timing control loop data is carried out while the read channel is operating in the test mode with an output of the data bits from a detector of the read channel being disabled during the test mode when the readback signal is being obtained from reading user data, and
• the at least one of gain control loop data or timing control loop data is extracted at a different sample rate than any gain control loop data or timing control loop data is extracted during the normal operation mode;
• transferring, via a data transfer bus, the extracted at least one of gain control loop data or timing control loop data from the readback signal obtained while reading user data stored on a data storage medium;
• and
• storing the transferred at least one of gain control loop data or timing control loop data obtained via the data transfer bus.